Flexible waveguides for optical coherence tomography

ABSTRACT

A system and method for depth-resolved imaging of a sample are presented. The system for depth-resolved imaging of a sample includes a substrate of substantially flexible material, a plurality of waveguides disposed on the substrate, an optical element disposed at a distal end of the plurality of waveguides, and one or more interferometers. Light is collected from the sample through the optical element and plurality of waveguides on the flexible substrate on its path to the one or more interferometers. The interferometers are configured to combine a reference light with the light received by at least a portion of the plurality of waveguides to resolve contributions from one or more depths of the sample. The system further includes a light guiding element coupled between the plurality of waveguides and the one or more interferometers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/761,054 filed Feb. 6, 2013, which claims the benefit under 35 U.S.C.§119(e) of U.S. provisional patent application Ser. No. 61/596,085,filed Feb. 7, 2012, the disclosures of which are incorporated byreference herein in their entireties.

BACKGROUND

1. Field

Embodiments described herein relate to the field of optical coherencetomography.

2. Background

Optical coherence tomography (OCT) is an imaging technique employed toview layers at different depths of a sample. The layers can be combinedto create a three-dimensional map of the sample's surface and depth upto a few millimeters. OCT imaging systems commonly collect informationof the sample's structure on a line-by-line basis. Each line scan (alsocalled an A-scan) provides one-dimensional in-depth information from aregion of the sample. By scanning the light beam laterally across thesample and then grouping several A-scans, two- and three-dimensionalmodels can be formed of the sample. The scanning is traditionallycarried out by mechanical movement of an optical element.

SUMMARY

Embodiments herein describe the use of a flexible substrate comprising aplurality of waveguides to be used with an OCT system.

In an embodiment, a system for depth-resolved imaging of a sampleincludes a substrate of substantially flexible material, a plurality ofwaveguides disposed on the substrate, an optical element disposed at adistal end of the plurality of waveguides, and one or moreinterferometers configured to combine a reference light with lightreceived by at least a portion of the plurality of waveguides to resolvecontributions from a given depth of the sample. The system furtherincludes a light guiding element coupled between the plurality ofwaveguides and the one or more interferometers.

In another embodiment, a system for depth-resolved imaging of a sampleincludes a substrate of substantially flexible material, a plurality ofwaveguides disposed on the substrate, an optical element disposed at adistal end of the plurality of waveguides, and one or moreinterferometers configured to combine a reference light with lightreceived by at least a portion of the plurality of waveguides to resolvecontributions from a plurality of depths of the sample. The systemfurther includes a light guiding element coupled between the pluralityof waveguides and the one or more interferometers.

An example method of making an optical coherence tomography systemincludes bonding a layer of semiconducting material to a layer offlexible material. The layer of semiconducting material is furtherthinned to a thickness of less than 10 microns. The method includespatterning the layer of semiconducting material to form a plurality ofwaveguides bonded to the layer of flexible material. The method alsoincludes bending the layer of flexible material having the plurality ofwaveguides bonded thereto and coupling the plurality of waveguides onthe bent flexible material to one or more interferometers used toperform optical coherence tomography.

Another example method of making an optical coherence tomography systemincludes patterning a layer of semiconducting material in a device layerof a SOI wafer to form a plurality of waveguides and depositing a firstlayer of flexible material over the plurality of waveguides formed inthe device layer. The SOI wafer includes a layer structure having thedevice layer, a buried oxide layer, and a handle layer. The handle layeris etched to substantially remove the handle layer followed by etchingthe buried oxide layer to substantially remove the buried oxide layer. Asecond layer of flexible material is deposited over the plurality ofwaveguides such that the plurality of waveguides are sandwiched betweenthe first and second layers of flexible material to form a flexibleoptical circuit. The method further includes bending the flexibleoptical circuit and coupling the plurality of waveguides on the bentflexible optical circuit to one or more interferometers used to performoptical coherence tomography.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIGS. 1A-D illustrate a plurality of waveguides on a flexible substrateand examples of bending the substrate, according to embodiments.

FIGS. 2A-D illustrate various views of the end of a catheter, accordingto embodiments.

FIG. 3 illustrates a block diagram of an OCT system, according to anembodiment.

FIG. 4 illustrates an example method, according to an embodiment.

FIG. 5 illustrates an example method, according to an embodiment.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present invention. It will be apparent to aperson skilled in the pertinent art that this invention can also beemployed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” etc., indicate that theembodiment described may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesdo not necessarily refer to the same embodiment. Further, when aparticular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

Overcoming the need for mechanical movement in an OCT scanner can berealized by using a large number of optical waveguides to collect lightfrom multiple points on a sample. Waveguides have previously beenfabricated in a planar lightwave circuit (PLC). The PLC may furtherinclude active elements to switch the path of the light betweendifferent waveguides or modulate the frequency of the light. However,waveguides fabricated in a PLC are, by definition, coplanar. Thishinders the use of a PLC-based OCT system for applications which requireradial or conical scanning (such as endoscopy). Furthermore, commonendoscopic or catheter probes can be smaller than 3 mm which limits thenumber of useable waveguides along the edge of a PLC.

In an embodiment of the present invention, the waveguides are providedon a flexible substrate. The flexible substrate allows for thewaveguides to be curled or bent into various shapes and more efficientlyfill a given area. For example, the flexible substrate may be curledinto a tight spiral or layered in an accordion-type shape. Once theflexible substrate has been manipulated into a particular form, it maybe placed into a housing or any other type of packaging for protectionand to help the substrate maintain its shape. For example, the flexiblesubstrate may be curled and subsequently placed into the cylindricalhousing of an endoscope to provide a dense array of waveguides withinthe housing.

FIG. 1A illustrates an example of a flexible substrate 102 comprising aplurality of waveguides 104. The flexible substrate may be a polymersuch as, for example and without limitation, polydimethylsiloxane (PDMS)or Parylene. The flexible substrate may also be a thin semiconductormaterial. Flexible substrate 102 may be sufficiently flexible so as toroll or bend without tearing.

Flexible substrate 102 is configured to adapt to various shapes as maybe useful for different applications. Once implemented onto flexiblesubstrate 102, waveguides 104 can then be arranged in a non-coplanarfashion while still allowing for focusing optics to direct the lightcoming out of the different waveguides 104 according to any desiredsampling pattern.

Waveguides 104 may be made from a single polymer material, or mayinclude a combination of polymer materials. For example, waveguides 104may be made from any one of SU-8, PMMA, PDMS, etc. Waveguides 104 mayalso be made from a semiconductor material such as silicon, or III-Vsemiconductor materials such as gallium arsenide or indium phosphide. Itshould be understood that impurities or other material combinations mayexist in the semiconductor materials, for example, tertiary orquaternary compounds.

Waveguides 104 may be fabricated on the surface of flexible substrate102. Surface patterning may involve a variety of lithographic maskingand etching techniques. Some examples of etching techniques includereactive ion etching, inductive coupled plasma etching, and wet chemicaletching. In another embodiment, waveguides 104 may be formed via bulkmicromachining in which the material of waveguides 104 is bonded toflexible substrate 102 and subsequently thinned to a final thicknessbelow 100 microns. Smaller single-mode or nearly single-mode waveguidesmay be thinned to a final thickness below 10 microns or below 1 micron.In one embodiment, the final thickness of waveguides 104 is about 3microns. Examples of thinning procedures include chemical mechanicalpolishing, bulk wet etching, and etching using a reactive gas such asxenon di-fluoride. Structural integrity may be ensured through theintroduction of carrier layers with appropriate tensile strength yetsufficient flexibility. Other wafer-level substrate transfer processescan be used to transfer waveguides formed as an optical device layeronto films such as substrate 102, as would be understood by one of skillin the art.

In another example, waveguides 104 may be embedded within flexiblesubstrate 102. Embedding waveguides 104 may provide better optical modecontainment within the waveguide due to the same or similar claddingmaterial surrounding each waveguide. Substrate 102 may be layered aroundwaveguides 104 in order to embed waveguides 104. In another example,waveguides 104 may be doped regions of a semiconductor layer with a topsemiconductor layer deposited over the doped layer to embed waveguides104. The semiconductor layers may be epitaxially grown or depositedusing chemical vapor deposition techniques.

Waveguides 104 may be disposed on or within substrate 102 such that allof the waveguides are parallel to each other. When waveguides 104 aredisposed onto a layer of a semiconductor or plastic substrate, they cancreate a flexible optical integrated circuit.

FIGS. 1B-D illustrate various ways that one may bend substrate 102 intodifferent shapes. FIG. 1B shows substrate 102, containing embeddedwaveguides 104, as rolled into a cylindrical shape. FIG. 1C showssubstrate 102 rolled into itself to create a spiral pattern ofwaveguides 104. FIG. 1D shows substrate 102 folded to create a layeredpattern. The circular and the spiral arrangement of substrate 102 areuseful when circular or conical scanning is required. FIGS. 1C and 1Dmay be particularly useful when dense three-dimensional scanningpatterns are desired. Other shapes may be considered as well withoutdeviating from the scope or spirit of the invention.

Such a combination of waveguides and flexible substrate, when bent, canbe combined with active elements to switch a light beam from onewaveguide to another. In such a manner, scanning may be performedwithout the need for mechanical scanning means. The active elements maybe based on electro-optic, thermo-optic, or carrier injection effects,for instance. In combination with terminal optics which focus the lightcoming out of each waveguide onto a different point of the sample'ssurface, an akinetic (without any moving parts) scanning system for OCTimaging can be achieved.

Waveguides defined inside traditional PLCs are, by definition, coplanar.This would hinder the use of an akinetic PLC-based scanning system forsome applications, such as endoscopic or catheter-based OCT systems,where special sample scanning schemes (e.g., radial scanning or conicalscanning) are needed. Line scanners are generally inefficient forobtaining radial or conical image information. The reason is that theoptical focusing system needed to convert the light beams from an arrayof co-planar waveguides in a PLC into a complex scanning pattern on thetissue is challenging to implement. In order to solve this problem, asystem may use a flexible waveguide system such as the embodimentsdescribed with respect to FIGS. 1A-1D.

FIGS. 2A-D provide various views of the end of a catheter or endoscopewhich includes a flexible waveguide system, according to an embodiment.Elements shown in broken lines are illustrated as being within housing201.

FIG. 2A illustrates a side view of a probe which includes a housing 201,a light guiding element 202, a flexible waveguide system 204, and anoptical element 206 disposed at distal end 208 of the probe. Lightguiding element 202 may be, for example, a single optical fiber or abundle of fibers. Alternatively, light guiding element 202 may be aplanar waveguide fabricated on a substrate. In one example, lightguiding element 202 is a waveguide fabricated on the same flexiblesubstrate as included in flexible waveguide system 204.

Flexible waveguide system 204 may include a plurality of waveguidessimilar to substrate 102 as described in FIGS. 1A-D. Additionally,flexible waveguide system 204 may be rolled into a cylindrical or spiralshape, for example. In an embodiment, a diameter of distal end 208 ofhousing 201 is less than 3 mm. In another example, the diameter ofdistal end 208 is less than 1 mm.

Optical element 206 directs light coming out of flexible waveguidesystem 204 onto a sample, according to an embodiment. Optical element206 may be, for example, any number of lenses and/or mirrors designed toguide light exiting distal end 208 towards a sample to be imaged.Optical element 206 may also be designed to collect light scattered backoff of the sample. In one embodiment, optical element 206 includes atleast one lens that is a gradient index (GRIN) lens. In another example,optical element 206 includes one or more spherical lens components.Distal end 208 may additionally or alternatively include a mirror todirect the light at a specific angle as it exits from distal end 208.Such a mirror may also be used for collecting light at a specific angleoff of the sample. Such a mirror may be a static mirror or a moveablemirror.

Light guiding element 202 is configured to transmit light betweenflexible waveguide system 204 and other optical components not disposedwithin housing 201, according to an embodiment. In another example,other optical components are coupled directly with flexible waveguidesystem 204 within housing 201. These other optical components mayinclude electrical or thermal modulators to change the frequency of thelight. Other optical components may also include one or moreinterferometers to constructively and/or destructively interfere thelight. The interferometers may be utilized for performing either time orfrequency domain optical coherence tomography.

Although only one light guiding element 202 is illustrated, it should beunderstood that any number of light guiding elements may be used toguide light from various waveguides within flexible waveguide system 204to other optical components of the system. Alternatively, one or moreoptical switches may be utilized to switch to a particular waveguide ofthe plurality of waveguides in flexible waveguide system 204 to couplelight into light guiding element 202.

FIG. 2B illustrates a front view looking into distal end 208 of theprobe, according to an embodiment. Optical element 206 may fill theregion at distal end 208. As such, flexible waveguide system 204 isshown behind optical element 206 using broken lines. Flexible waveguidesystem 204 is wrapped in a tube-like shape, according to an embodiment.

FIG. 2C illustrates a top view of the probe that includes flexiblewaveguide system 204 and optical element 206 within housing 201,according to an embodiment. Light guiding element 202 can be seenconnecting to flexible waveguide system 204 within housing 201.

FIG. 2D illustrates a perspective view of the probe end. A cylindricalshape of flexible waveguide system 204 disposed within the cylindricalhousing 201 of the probe is observed, according to an embodiment. Lightguiding element 202 may be coupled to a portion of flexible waveguidesystem 204, according to an embodiment, or it may be coupled to allwaveguides in flexible waveguide system 204. A single light guidingelement 202 is illustrated; however, a plurality of light guidingelements may be disposed around substantially the entire circumferenceof flexible waveguide system 204 to capture light from the waveguides offlexible waveguide system 204.

Another optical element may be used to direct the light from lightguiding element 202 to one or more of the waveguides on flexiblewaveguide system 204. For example, a multiplexer may be disposed betweenlight guiding element 202 and flexible waveguide system 204. In anotherexample, the multiplexer is disposed on the substrate of flexiblewaveguide system 204. The multiplexer may include one or more of opticalswitches, circulators, beam steering modulators, etc. The multiplexerallows for the integration of many optical paths via flexible waveguidesystem 204 with a single optical path via light guiding element 202.

FIG. 3 illustrates a diagram of an example OCT system 300 which includesthe use of a flexible waveguide system, according to an embodiment. OCTsystem 300 includes an optical sensor 302, one or more interferometers304, a light guiding element 306 which couples interferometers 304 to amultiplexer 308, a flexible waveguide system 310, and an optical element312. In the example illustrated in FIG. 3, optical element 312 is a GRINlens. Not shown in FIG. 3 is a light source which would produce light tobe directed onto a sample 314 at some distance from optical element 312.The light produced from the light source may also be directed down lightguiding element 306 and through flexible waveguide system 310 on its wayto sample 314. In an embodiment, the light source may also be used as areference light.

In one embodiment, one or more interferometers 304 are used to performtime domain optical coherence tomography (TD-OCT). The optical pathlength of a reference arm of the one or more interferometers 304 ismodulated so as to modulate a reference beam of light. When themodulated reference beam is combined with a beam of light received fromsample 314, the resulting interference resolves signal contributionsfrom a given depth of sample 314. The optical path length of thereference arm may be changed over time to yield image data at differentdepths of sample 314. The modulation of the optical path length istraditionally performed by mechanically moving one or more mirrors inthe path of the reference light beam. However, other modulationtechniques are to be considered as well, such as, for example,thermo-optic or electro-optic modulators coupled to a waveguide foraltering the optical path length of the light within the waveguide.

In another embodiment, one or more interferometers 304 are used toperform frequency domain optical coherence tomography (FD-OCT). Whenperforming FD-OCT, multiple depths of sample 314 may be analyzedsubstantially simultaneously by, for example, using a plurality ofspectrally separated detectors at optical sensor 302. A Fouriertransform may be performed on the signal received by optical sensor 302to resolve various signal components associated with various depths ofsample 314. In one example, performing FD-OCT allows for acquiring imageinformation at various depths without the need for changing the opticalpath length of the reference arm in the one or more interferometers 304.

Multiplexer 308 may be configured to transmit light through a firstsubset of waveguides on flexible waveguide system 310 while receivinglight scattered back from sample 314 from a second subset of waveguideson flexible waveguide system 310. As light is reflected back from sample314 into optical element 312, it travels back along light guidingelement 306 to one or more interferometers 304, according to oneembodiment. In another example, the light may travel back to one or moreinterferometers 304 using a different path than via light guidingelement 306. One or more interferometers 304 may combine the light witha reference light to constructively and/or destructively interfere thelight. The resolved light associated with either a given depth of sample314 when performing TD-OCT, or a plurality of depths of sample 314 whenperforming FD-OCT, is collected at optical sensor 302.

Sample 314 may be a tissue sample, for example, a lining of a heart or acolon. A plurality of locations on sample 314 may be imaged at one timedue to the plurality of waveguides present in flexible waveguide system310. Additionally, radial and/or conical image information may becollected from sample 314 due to the circular arrangement of waveguides.

FIG. 4 illustrates a flowchart depicting a method 400 for fabricating anoptical coherence tomography system, according to an embodiment of theinvention. The fabrication of the system may involve fabricating aplurality of waveguides on a flexible material such as thoseillustrated, for example, in FIGS. 1B-1D. It is to be appreciated thatmethod 400 may include operations additional to those shown, or performthe operations in a different order than shown.

Method 400 begins at step 402 where a semiconductor layer is bonded to alayer of flexible material, according to an embodiment. Thesemiconductor may be, for example, silicon or gallium arsenide. Theflexible material may be, for example, PDMS or Parylene. The bonding maybe anodic, or may use other techniques as would be known by one skilledin the relevant art(s) given the description herein.

Method 400 continues with step 404 where the semiconductor layer isthinned. The thinning may produce a semiconductor layer having athickness of less than 10 microns. In one embodiment, the finalthickness of the semiconductor layer is around 3 microns. Chemicalmechanical polishing (CMP) may be utilized for the thinning procedure.It should be understood that step 404 may not be necessary in a casewhere the semiconductor layer is already thin enough when initiallybonded to the flexible material.

In step 406, the semiconductor layer is patterned to form waveguides onthe flexible material, according to an embodiment. The patterning of thesemiconductor layer may involve conventional lithography techniques tofirst pattern a photoresist layer over the semiconductor layer andsubsequently etch the exposed semiconductor material to form thewaveguides. Alternatively, a hard mask material such as silicon nitridemay be used in place of photoresist. In one embodiment, the waveguidesare formed as substantially parallel lines on the flexible material.After the waveguides are formed, a cladding material may be deposited oradded over the top of the waveguides to further confine the light modewithin the waveguide core.

In step 408, the layer of flexible material having the plurality ofwaveguides is bent into a particular shape, according to an embodiment.In one example, the flexible material may be bent into a cylindrical orspiral shape as illustrated in FIGS. 1B and 1C respectively. A generallycircular shape may aid the placement of the flexible waveguides into atubular-like apparatus such as a catheter or endoscope. Other shapes maybe considered as well to more conveniently place the flexible waveguidesinto various devices. The various bent shapes of the waveguides candecrease the form factor of an optical system and also provideadditional imaging techniques not readily available from strictlyco-planar waveguides.

In step 410, the plurality of waveguides are coupled to one or moreinterferometers, according to an embodiment. The one or moreinterferometers combine the light received from at least a portion ofthe plurality of waveguides with a reference beam of light to performOCT imaging. The coupling between the waveguides and the interferometersmay involve any number of light guiding elements, lenses, mirrors,multiplexers etc. For example, a light guiding element, such as anoptical fiber, may be used to couple light from the plurality ofwaveguides to the one or more interferometers. In another example, oneor more lenses may be used to focus the light exiting from the pluralityof waveguides onto a light guiding element, or directly onto an opticalelement integrated as part of the one or more interferometers.

FIG. 5 illustrates a flowchart depicting a method 500 for fabricating anoptical coherence tomography system, according to another embodiment ofthe invention. It is to be appreciated that method 500 may includeoperations additional to those shown, or perform the operations in adifferent order than shown.

Method 500 begins at step 502 where a device layer of aSilicon-On-Insulator (SOI) wafer is patterned to form waveguides,according to an embodiment. The SOI wafer may include a semiconductingdevice layer, a buried silicon dioxide layer, and a handle layer thatmay be up to several hundred microns thick. It should be appreciated,however, that the SOI wafer and fabrication process described in method500 should not be limited to using silicon as the device layer, and thatother semiconducting and polymer materials could be used as well. Asabove, the patterning of the semiconductor layer may involveconventional lithography techniques to first pattern a photoresist layerover the semiconductor layer and subsequently etch the exposedsemiconductor material to form the waveguides. Alternatively, a hardmask material such as silicon nitride may be used in place ofphotoresist. In one embodiment, the waveguides are formed assubstantially parallel lines on the flexible material. The device layermay have a thickness of, for example, less than 10 microns. In oneembodiment, the final thickness of the device layer is around 3 microns.After the waveguides are formed, a cladding material may be deposited oradded over the top of the waveguides to further confine the light modewithin the waveguide core. Other material layers or process steps couldbe added for additional electrical or optical functionality.

Method 500 continues at step 504, where a thin layer of flexiblematerial is deposited on top of the SOI wafer ensuring good adhesion tothe device layer where the waveguides have been defined, according to anembodiment. The flexible material may be, for example, PDMS or Parylene.Deposition will be done through spinning, layer transfer based ontemperature and pressure application or other methods known by oneskilled in the relevant art(s) given the description herein. Adhesionbetween the flexible material and the device layer where the waveguideshave been defined may be ensured through surface preparation using O₂plasma or other means, such as, for example, intermediate adhesionpromotion layers. Other techniques for improving the adhesion may beused as would be known by one skilled in the relevant art(s) given thedescription herein.

Method 500 continues with step 506 where the SOI wafer with the flexiblematerial on top is attached to a carrier substrate, according to anembodiment. Such attachment may be achieved through a thin adhesivelayer, including a photoresist layer. The adhesive may be selected so asto be easily removed with a solvent without adversely affecting theflexible layer or the waveguides. Such a solvent may be, for example,acetone, methanol, isopropanol or any other organic or inorganicsolvent.

Method 500 continues with step 508 where the handle layer of the SOIwafer is etched, using the buried oxide layer as a stop layer. Thisetching step can be done using wet anisotropic etching, wet isotropicetching, deep reactive ion etching, other plasma-based etching processesor other means known by one skilled in the relevant art(s) given thedescription herein. This etching step can be modulated by a lithographystep, where solid silicon islands are protected through a soft or hardmask. Such rigid islands may be left on the buried oxide in as far asthis may be needed to strengthen the structure for packaging, functionalor other application needs.

In step 510, the buried oxide layer is subsequently etched away using anetching solution, according to an embodiment. In one example, theetching solution may be chosen to have either a zero or negligible etchrate for the waveguide material to protect the waveguides. Such anetchant may be based on hydrofluoric acid (HF), but other compositionsare possible as would be known to one skilled in the relevant art(s).

In step 512, another flexible layer is deposited on the exposed siliconwaveguides, according to an embodiment. Step 512 is optional, however,the additional flexible layer sandwiches the waveguides in order toprotect the optical circuit, add additional mechanical strength, andimprove the cladding around the waveguides. In this step, furtherpatterning of the flexible optical circuit is possible, wherebyarbitrary shapes may be defined in the substrate. Such shapes may beused to enhance flexibility, simplify packaging, or other purposes.Patterning may be performed using lithography masks to protect theflexible optical circuit from the etching step. Etching of the flexibleoptical circuit may be achieved, for example, through plasma-basedetching processes.

In step 514, the flexible optical circuit is released from the carriersubstrate, according to an embodiment. The release may occur on the dielevel after cutting the flexible optical circuit bonded to the carriersubstrate into dies of adequate size. The release may be performed byusing a solvent that dissolves the adhesion layer only.

In step 516, the flexible optical circuit is bent into a particularshape, according to an embodiment. In one example, the flexible opticalcircuit may be bent into a cylindrical or spiral shape as illustrated inFIGS. 1B and 1C respectively. A generally circular shape may aid theplacement of the flexible waveguides into a tubular-like apparatus suchas a catheter or endoscope. Other shapes may be considered as well tomore conveniently place the flexible waveguides into various devices.The various bent shapes of the waveguides can decrease the form factorof an optical system and also provide additional imaging techniques notreadily available from strictly co-planar waveguides.

In step 518, the plurality of waveguides on the flexible material arecoupled to one or more interferometers, according to an embodiment. Theone or more interferometers combine the light received from at least aportion of the plurality of waveguides with a reference beam of light toperform OCT imaging. The coupling between the waveguides and theinterferometers may involve any number of light guiding elements,lenses, mirrors, multiplexers etc. For example, a light guiding element,such as an optical fiber, may be used to couple light from the pluralityof waveguides to the one or more interferometers. In another example,one or more lenses may be used to focus the light exiting from theplurality of waveguides onto a light guiding element, or directly ontoan optical element integrated as part of the one or moreinterferometers.

Some embodiments of a flexible waveguide system described herein providecertain structural advantages. For example, waveguides disposed onto aflexible substrate may have a size advantage over standalone opticalfibers, in that the waveguides disposed on a substrate can be made muchsmaller than a standalone fiber because the substrate can be used asstructural support for the waveguides. Utilizing smaller waveguidesallows for packing more waveguides over a given area. As such, moreindividual data points may be taken for a given surface area. Further,once the waveguides have been disposed on a substrate, the waveguidesmay be organized into a specific, stable shape, which may not bepossible or easy with standalone optical fibers.

Embodiments of the present invention have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

What is claimed is:
 1. An optical coherence tomography system fordepth-resolved imaging of a sample, comprising: a substantially flexiblepolymer substrate bonded to a layer of semiconducting material, whereinthe layer of semiconducting material is patterned to form a plurality ofwaveguides, and wherein the substrate is bent; an optical elementdisposed at a distal end of the plurality of waveguides; one or moreinterferometers configured to combine a reference light with lightreceived by at least a portion of the plurality of waveguides on thebent substrate to resolve contributions from a given depth of the sampleusing optical coherence tomography; and a light guiding element coupledbetween the plurality of waveguides on the bent substrate and the one ormore interferometers.
 2. The system of claim 1, wherein the polymersubstrate comprises PDMS.
 3. The system of claim 1, wherein the polymersubstrate comprises parylene.
 4. The system of claim 1, wherein theplurality of waveguides are composed of at least one of silicon, galliumarsenide, and indium phosphide.
 5. The system of claim 1, furthercomprising an optical multiplexer configured to switch a path of lightfrom the light guiding element to one or more of the plurality ofwaveguides.
 6. The system of claim 1, wherein the substrate isconfigured to be rolled into a substantially cylindrical shape.
 7. Thesystem of claim 6, wherein the substrate is disposed within asubstantially cylindrical housing.
 8. The system of claim 1, wherein theoptical element comprises one or more mirrors.
 9. The system of claim 1,wherein the optical element comprises one or more lenses.
 10. The systemof claim 9, wherein at least one of the one or more lenses is a gradientindex lens.
 11. The system of claim 1, wherein the light guiding elementis an optical fiber.
 12. The system of claim 1, wherein the plurality ofwaveguides comprise single-mode waveguides.
 13. An optical coherencetomography system for depth-resolved imaging of a sample, comprising: asubstantially flexible polymer substrate bonded to a layer ofsemiconducting material, wherein the layer of semiconducting material ispatterned to form a plurality of waveguides, and wherein the substrateis bent; an optical element disposed at a distal end of the plurality ofwaveguides; one or more interferometers configured to combine areference light with light received by at least a portion of theplurality of waveguides on the bent substrate to resolve contributionsfrom a plurality of depths of the sample using optical coherencetomography; and a light guiding element coupled between the plurality ofwaveguides on the bent substrate and the one or more interferometers.14. The system of claim 13, further comprising an optical multiplexerconfigured to switch a path of light from the light guiding element toone or more of the plurality of waveguides.
 15. The system of claim 13,wherein the substrate is configured to be rolled into a substantiallycylindrical shape.
 16. The system of claim 15, wherein the substrate isdisposed within a substantially cylindrical housing.
 17. The system ofclaim 13, wherein the depth-resolved imaging includes optical coherencetomography (OCT).
 18. The system of claim 13, wherein the plurality ofwaveguides comprise single-mode waveguides.
 19. The system of claim 1,wherein each waveguide in the plurality of waveguides has a thicknessbetween 1 and 10 microns.
 20. The system of claim 13, wherein eachwaveguide in the plurality of waveguides has a thickness between 1 and10 microns.